Coating thickness gauge

ABSTRACT

A modular coating thickness gauge includes a probe which generates a signal representative of coating thickness, a PCMCIA card connected to the probe for converting the signal into a standard PCMCIA output format, and a portable computing unit for receiving the signal via the PCMCIA card. The gauge allows the on-site user to alternately record coating thickness measurement data and descriptive textual or graphical data relating to each coating thickness measurement.

BACKGROUND

1. Field of the Invention

The present invention relates to coating thickness gauges and moreparticularly to a novel method and apparatus for measuring and recordingcoating thickness data and associated descriptive data through agraphical user interface.

2. Description of the Related Art

The art of measuring the thickness of a coating on a substrate hasproduced a wide variety of coating thickness gauges for measuring avariety of materials. In general, coating thickness gauges include aprobe which produces an electronic signal responsive to a measuredphysical quantity representative of a coating thickness. For example,when measuring the thickness of an electrically nonconductive coating ona conductive substrate, the probe can include an inductor whichregisters a change in impedance based on its proximity to the conductivesubstrate. The impedance change of the inductor is reflected by a changein frequency in an LC oscillator which can be mathematically related tothe thickness of the coating.

Conventional coating thickness gauges have also provided the capabilityof transforming the electronic signal representative of coatingthickness into digital data and of storing a number of data points forlater downloading and analysis. Typically, the coating thicknessmeasurements are later sequentially correlated to a written descriptionof the article being measured. Such a procedure, however, requires theuser to manually keep track of which data points correspond to whichlocations on the object being measured, and are thus time consuming andsusceptible to recording errors.

Thus, although coating thickness gauges have been developed to providevery accurate digital readings, the industry has not yet produced acoating thickness gauge with a user interface which facilitatesrecording and analysis of data, despite the ongoing advances in computertechnology. Prior to the present invention, there was a need in the art,therefore, for a method and apparatus for measuring and recordingcoating thickness data which is easy to use and which ensures accuracyand reliability in the recording of measurements.

OBJECTS AND SUMMARY

It is an object of the invention to provide a novel coating thicknessgauge which allows a user to record thickness measurement data alongwith descriptive data through a user interface on a computer screen.

It is a further object of the invention to improve the accuracy ofcoating thickness measurement data by providing an apparatus whichallows a user to alternate between recording a coating thicknessmeasurement data point and recording descriptive textual or graphicaldata relating to the data point.

It is a further object of the invention to provide a modularized coatingthickness apparatus which includes a probe which produces an electricsignal representative of a measured coating thickness and a PCMCIA cardwhich receives the electric signal and converts the electric signal intoa digital data signal in a standard PCMCIA output format. The coatingthickness apparatus preferably includes a portable computing unit orPersonal Digital Assistant (PDA) with a port for receiving the PCMCIAcard and a screen for providing a graphical user interface.

An exemplary method according to the present invention includes thesteps of obtaining a plurality of coating thickness values with a probeelectrically connected to an electronic memory, recording in theelectronic memory the plurality of coating thickness values, andrecording in the electronic memory a plurality of descriptive dataunits, each descriptive data unit being associated with one of thecoating thickness values and defined, for example, with reference to anelectronic pictorial representation of the coated article. The steps ofrecording the coating thickness values and of recording the descriptivedata units may be performed alternately.

Exemplary embodiments of the invention provide the on-site user with thepower of a personal computer together with an easy-to-use interface thatdoes not require a keyboard. Among other advantages, the gauge improvesthe accuracy and reliability of coating thickness measurements, providesthe flexibility of plugging in any probe (e.g., magnetic, eddy current,ultrasonic, etc.) to any PCMCIA-compatible device, and allows the userto perform data analysis on-site.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention will be more readily understood upon reading the followingdetailed description in conjunction with the drawings in which:

FIG. 1 is a perspective view of a coating thickness gauge according toan exemplary embodiment of the invention;

FIG. 2 is a schematic diagram of an exemplary PCMCIA card/probe unit;

FIG. 3a is an enlarged view of a portion of a first exemplary probeassembly;

FIG. 3b is a diagram of a second exemplary probe assembly;

FIG. 4 is a schematic diagram of a portable computing unit;

FIG. 5 is a diagram of an exemplary control display on the portablecomputing unit; and

FIG. 6 is a diagram of an exemplary output display on the portablecomputing unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of a coating thickness gauge according toan exemplary embodiment of the invention. The portable gauge 10comprises a probe 20 connected by a cable 30 to an interface unit 40such as a Personal Computer Memory Card International Association(PCMCIA) card. The PCMCIA card 40 is adapted to communicate with aportable computing unit 50 via a port 60. The portable computing unit 50is small enough to be held comfortably in the palm of one's hand.However, it preferably includes a relatively large screen display 70 toprovide a graphical interface to the user. The screen 70 is preferably,though not necessarily, a touch-sensitive screen which can be activated,for example, with an index finger or with any suitable pointed writinginstrument 80. The portable computing unit 50 can be of the typegenerally known as a Personal Digital Assistant. The Apple NEWTON®,which provides a graphical user interface without a keyboard, is apreferred example of such a portable computing unit 50.

The PCMCIA card 40 can be adapted to support a wide variety ofperipheral devices, and due to its versatility, allows virtually anytype of probe 20 to be incorporated into the thickness gauge 10. For thepurpose of illustration, two exemplary embodiments will now be describedbriefly in which a known type of probe 20 is implemented to measure thethickness of a coating on substrate. However, those skilled in the artwill recognized that the PCMCIA card 40 can be adapted to support manyother types of probes 20 in conjunction with the portable computing unit50.

According to one embodiment, as shown in FIG. 2 and as further describedin commonly owned U.S. Pat. No. 5,293,132, entitled "Coating ThicknessMeasurement Gauge", which is hereby incorporated herein by reference,the probe 20 of the coating thickness gauge 10 can be the inductor 75 ofan LC oscillator 85 of suitable, known type. The LC oscillator 85 allowsfor the measurement of the thickness of an electrically nonconductivecoating on an electrically conductive substrate. The inductor 75 can bea simple air-core solenoid-type coil. The phrase "air-core" is meant torefer to a coil having a core made of nonmagnetic, nonmetallic material.In practice, the wire is wound around a nonmagnetic, nonmetallic rod.During measurement, a probe structure housing the probe is placed incontact with the surface of the coating such that the separation of thecoil 75 and the electrically conductive substrate is a function of thegeometry of the probe structure and the coating thickness.

The impedance of the coil 75 varies with its proximity to theelectrically conductive substrate resulting in a corresponding variationin the oscillation frequency of the LC oscillator 85. This frequency isdetermined by a counter 90 which is used in conjunction with amicroprocessor 100. For instance, a timing loop may be programmed intothe microprocessor 100 such that it resets the counter 90 at thebeginning of the timing loop and measures the period of time elapseduntil a predetermined number of oscillations has occurred as indicatedby an overflow signal. The number of measured oscillations should belarge enough to achieve the desired accuracy.

The relationship of the change in frequency of the oscillator 85 to thecoating thickness is dependent on the particulars of the geometry of theprobe assembly 20, shown in expanded detail in FIG. 3a. The mostsignificant parameters affecting the relationship of the change infrequency to the coating thickness are the diameter r of the coil 75,the number of turns of the coil 75, the height I of the coil 75, thegauge of the wire as it affects the dimension b, and the material of thewound wire. Furthermore, the relationship is different depending on thematerial composition of the substrate. For a nonmagnetic substrate suchas aluminum, the relationship may be approximated by the fourth-orderpolynomial:

    Y=A.sub.0 +A.sub.1 F+A.sub.2 F.sup.2 +A.sub.3 F.sup.3 +A.sub.4 F.sup.4

where the coefficients A₀₋₄ are determined by the geometry of the probe20 and the electrical characteristics of the substrate.

For a six-turn single layer wound coil using 26-gauge copper wire, thecoefficients A₀₋₄ may be empirically determined and represented asfollows for nonmagnetic aluminum substrates, with F representing thefrequency change in KHz and Y representing the thickness in microns:

    Y=10090.44-(26.965)F+(3.0195×10.sup.-2)F.sup.2 -(1.60-374×10.sup.-5)F.sup.3 +(+3.25473×10.sup.-9)F.sup.4

A complete set of coefficients A₀₋₄ can be stored in a ROM portion 110associated with the microprocessor unit 100 during production of thethickness 10 gauge for any desired substrate material. For example, anadditional set of coefficients B₀₋₄ can be stored for use with magneticsubstrates. Thus, upon selection by the user of one of the substratematerials stored in memory, the coefficients associated with theselected substrate material can be recalled from the ROM 110 andemployed along with the measured frequency change in the appropriateequation shown above for determining coating thickness.

According to a second exemplary embodiment, a second gauge probe can beused in conjunction with the present invention to determineautomatically, with a single probe, the substrate characteristics, andto effect a measurement of the coating thickness on that substrate. Sucha probe is described for example in commonly owned U.S. Pat. No.5,343,146, entitled "Combination Coating Thickness Gauge Using aMagnetic Flux Density Sensor and an Eddy Current Search Coil", which ishereby incorporated herein by reference. The probe tests for a ferroussubstrate, measuring the temperature-compensated magnetic flux densityat a pole of a permanent magnet using a Hall effect magnetic sensor anda thermistor. FIG. 3b shows a probe 25 which includes a permanent magnet35, a Hall effect magnetic sensor 45, and a thermistor 55. The magneticflux density and temperature measurements are converted into atemperature-compensated magnetic flux density value that is proportionalto the coating thickness on the ferrous substrate. If no ferroussubstrate is detected, the coating thickness gauge automaticallyswitches over to test for a conductive nonferrous substrate, measuringthe effects of eddy currents generated in the conductive nonferroussubstrate by the coating thickness gauge magnetic fields using an eddycurrent search coil 65, as shown in FIG. 3b. The eddy currentmeasurements are converted into an eddy current frequency value that isproportional to the coating thickness on the conductive nonferroussubstrate.

Various other types of known probes may also be incorporated into thepresent invention, for example probes which measure coating thicknesseson ferrous substrates with a magnetic induction technique using twocoils and a ferrous core. As discussed with regard to the firstembodiment, the PCMCIA card 40 can be adapted to include hardwareelements such as a counter or a ROM chip to support a desired coatingthickness gauge probe. The gauge electronics 120 in FIG. 2 are thusintended to generally represent a capacity of the PCMCIA card 40 toinclude hardware elements to support any type of gauge probe. Forexample, as will be readily appreciated by those skilled in the art, thePCMCIA card 40 can be modified by one skilled in the art to includehardware to support probes which measure thicknesses of nonmagneticcoatings on ferrous substrates, nonconductive coatings on nonferroussubstrates, combination probes which measure both, or probes whichultrasonically measure coating thicknesses on nonmetals.

In addition to the hardware support elements 120 included in the PCMCIAcard 40 for a particular application, The PCMCIA card 40 also includesthe microprocessor 100 and a PCMCIA interface 130 which creates astandardized communication path from the microprocessor 100 to theportable computing unit 50. Included in the PCMCIA interface 130 is aUniversal Asynchronous Receiver Transmitter (UART) 140, an I/O devicewhich sends and receives information in bit-serial fashion. Themicroprocessor 100, in conjunction with the supporting hardware 120,converts the signal from the probe 20 into a digital representation of acoating thickness which is transmitted through the UART 140 to theportable computing unit 50 in a standardized PCMCIA format. For brevity,the details of this process are omitted, as those skilled in the art arecapable of adapting a particular signal to the PCMCIA format.

The physical attributes and internal operation of the PCMCIA card 40 aredefined in detail by the Personal Computer Memory Card InternationalAssociation, which updates the PCMCIA specifications periodically. ThePCMCIA standard includes detailed specifications regarding the physicalattributes of the card such as dimensions and mechanical tolerances,card interface information such as signal definitions for the connectingpins 125 of the PCMCIA card, and data organization on the card. Becausethe PCMCIA card is a standard interface, the present invention providesa versatile coating thickness gauge which can be used in a wide varietyof hardware environments.

The portable computing unit 50 receives the PCMCIA card 40 via a port 60to communicate with the probe 20. The portable computing unit 50includes, among other elements, a microprocessor 150 for controlling theoperations of the coating thickness gauge 10. See FIG. 4. The portablecomputing unit 50 can be programmed, for example, to automaticallyrecognize the type of probe which is connected to the portable computingunit 50. The microprocessor 150 is associated with a memory 160 whichcan store computer programs which control the operation of the gauge 10.The microprocessor 150 exchanges data with the memory 160 and with theuser via the screen 70 which is large enough to provide a graphicalinterface for the user. The versatility provided by the memory 160, themicroprocessor 150, the large screen 70, and the standard PCMCIAinterface thus provide the coating thickness gauge 10 of the presentinvention with many important advantages. Exemplary embodiments of theinvention, for example, provide the user with the ability to performcomplete data analysis or statistical process control on-site, theflexibility of using any probe with any PCMCIA-compatible portablecomputing unit 50, and the capability of providing a sophisticated userinterface which allows the user to easily annotate coating thicknessmeasurements with descriptive textual and graphical data.

According to one exemplary method of the invention, a user of the gauge10 alternates between recording a thickness measurement reading with theprobe 20 and entering descriptive data via the screen 70. Thedescriptive data can be entered in a number of ways. For example, avirtual typewriter keyboard can be graphically simulated on the screen70 for entry of descriptive comments relating to a particular thicknessmeasurement using an index finger or a pointed writing instrument 80.Alternatively, the portable computing unit 50 can be adapted to converta handwritten image, created by handwriting on the screen with thewriting instrument 80, into textual data. The process of converting ahandwritten image of "electronic ink" or typed letters into digitaltextual data, which has been incorporated into the Apple NEWTON®,greatly facilitates the entry of descriptive data associated with aparticular coating thickness measurement. The ability to label all orselective individual data points with descriptive text also enhances thereliability of the measured coating thickness data by ensuring that datapoints are properly labeled and by allowing the user to immediatelyrecord any abnormalities as measurements are taken.

According to a further exemplary method, a two- or three-dimensionalimage of the object to be measured can be created on the screen 70 bythe user as a reference for input coating thickness data points.According to this method, a user first recalls or sketches a diagram ofthe object to be measured on the screen 70 of the portable computingunit 50 using the writing instrument 80. This process can be facilitatedwith a program, included in the Apple NEWTON, which transformsuser-created images into various geometrical forms such as rectanglesand circles. The drawing is then stored in the memory 160 as a referencefor the measured thickness values. As coating thickness values areobtained with the probe 20, the user identifies, with reference to thescreen drawing, the locations on the object at which the coatingthickness values were obtained. In addition, the user can input for anycoating thickness value, a textual description relating to the measureddata point. FIG. 1 is an example which depicts a drawing of a coatedpipe 170 which a user would measure to obtain coating thickness valuesat various locations. After taking a measurement of the actual pipe withthe probe 20, the user simply indicates the location of the data pointwith reference to the pictorial representation on the screen 70 usingthe writing instrument. The screen thus serves as a graphical interfaceto record the location of data points 180, as shown in FIG. 1.

The large touch-sensitive screen 70 of the portable computing unit 50can be further adapted to facilitate operation of the coating thicknessgauge 10 with a number of virtual buttons. As shown in FIG. 5, thescreen 70 can include several virtual buttons 190 which, for example,allow the user to enter a memory mode to begin storing thicknessmeasurements, enter high and low tolerance limits, command the gauge tocompute and display statistics on the data thus obtained, enterparameters specifying a particular process used in applying a coating,specify units for the coating thickness readings, or any other desiredfunction. The process control button can be used for, among otherfunctions, labeling any batch with a particular process used in coating.This feature facilitates data analysis by allowing the user to analyze agroup of batches associated with the same coating process. Calibrationbuttons 200 are provided to calibrate the gauge when a reading differsfrom a known thickness.

At the top of the screen 70, a display section 210 may be provided whichdisplays thickness readings with units, an indicator of whether aferrous or nonferrous material was measured, a textual description of aparticular batch, and a label for a particular process used in coating.The screen 70 shown in FIG. 5 is of course intended to provide anexample illustrating the versatility of one embodiment of an exemplarycoating thickness gauge. It will be readily appreciated by those skilledin the art, however, that many modifications in the screen interface canbe affected without departing from the scope of the invention.

The screen 70 can also be adapted to provide graphical output, whichadvantageously allows the on-site user to use statistical processcontrol in analyzing coating thickness measurements. FIG. 6 shows anexemplary output screen which includes graphs 220 and 230 of x-bar andrange for a set of batches, a histogram 240, and a list of desiredstatistics 250 for the stored readings. The x-bar graph 220 shows on thescreen 70 a computed average thickness value for each batch. The rangegraph 230 shows a computed difference in thickness between the greatestand least measured thickness in a particular batch. These graphs thusallow the user to easily monitor any anomalies or trends in the coatingprocess. Moreover, according to an exemplary embodiment of theinvention, the user can access any annotations or other descriptive dataassociated with a batch or thickness measurement simply by touching thedisplayed batch number, data point, or other indicia on the screen 70with the writing instrument 80. This capability allows the user todetermine, for example, whether anomalies illustrated in the outputgraphs are associated with any anomalies described in annotationsrecorded during measurement.

The histogram 240 provides an additional visual indicator of theconsistency of recorded coating thickness measurements. The list ofstatistics 250 can include, among other parameters, a standard deviationcalculated from measurements of selected batches, a maximum and aminimum reading, upper and lower set limits (USL, LSL) set by the user,and upper and lower control limits (UCL, LCL) which represent theaverage thickness plus or minus three standard deviations. Like thescreen of FIG. 5, the output screen in FIG. 6 is, of course, intended toshow one embodiment which may be modified, for example, to accommodateother statistical process control operations without departing from thescope of the invention.

The present coating thickness gauge according to exemplary embodimentsof the invention thus provides many important advantages in obtainingcoating thickness measurement data. By combining a portable computingunit such as a Personal Digital Assistant with a coating thickness gaugeprobe via a PCMCIA interface, the invention greatly enhances thecomputing options available for obtaining and processing coatingthickness measurements on-site. Thus, the user may perform dataanalysis, enter descriptive comments, control the gauge with icons, andgenerally harness the power of a large display, resident software, andregular upgrades of the portable computing unit. Moreover, theseadvantages are provided in a coating thickness gauge which issubstantially less expensive to manufacture than commercially availablegauges.

The above-described exemplary embodiments are intended to beillustrative in all respects, rather than restrictive, of the presentinvention. Thus the present invention is capable of many variations indetailed implementation that can be derived from the descriptioncontained herein by a person skilled in the art. All such variations andmodifications are considered to be within the scope and spirit of thepresent invention as defined by the following claims.

What is claimed is:
 1. A method of recording coating thicknessmeasurements, comprising the steps of:obtaining a plurality of coatingthickness values with a probe electrically connected to an electronicmemory; recording in the electronic memory the plurality of coatingthickness values; and recording in the electronic memory a plurality ofdescriptive data, each descriptive data is associated with a respectiveone of the coating thickness values and provides information concerningthe respective one coating thickness value.
 2. The method of claim 1,wherein the steps of recording the coating thickness values and ofrecording the descriptive data are performed alternately.
 3. The methodof claim 1, wherein the coating thickness values are transmitted to theelectronic memory via a PCMCIA card.
 4. The method of claim 1, whereinthe descriptive data comprise text.
 5. The method of claim 1, whereinthe descriptive data are recorded by transforming text handwritten on acomputer screen with a writing instrument into digital data.
 6. Themethod of claim 1, wherein the descriptive data are defined withreference to an electronic pictorial representation of a coated article.7. The method of claim 6, wherein the descriptive data representlocations on the electronic pictorial representation of the coatedarticle.
 8. The method of claim 1, further comprising the step ofdisplaying a plurality of indicia on a graph on a video display screen,the indicia representing the plurality of coating thickness values. 9.The method of claim 8, further comprising the step of retrieving one ofthe descriptive data by selecting on the graph one of the indicia. 10.An apparatus for measuring a coating thickness, comprising:a probe whichgenerates a first signal representative of a measured coating thickness;and a PCMCIA card connected to the probe and which receives the firstsignal from the probe, the PCMCIA card including means for convertingthe first signal into a second signal which is compatible with astandard PCMCIA output format.
 11. The apparatus of claim 10, whereinthe probe comprises an LC oscillator.
 12. The apparatus of claim 11,wherein the PCMCIA card includes a counter which measures a frequency ofthe LC oscillator.
 13. The apparatus of claim 10, wherein the probecomprises a permanent magnet and a Hall sensor.
 14. The apparatus ofclaim 13, wherein the probe further comprises an eddy current searchcoil.
 15. The apparatus of claim 10, wherein the probe includes meansfor discriminating between a ferrous and a nonferrous substrate uponwhich the coating is coated.
 16. The apparatus of claim 10, furthercomprising a portable computing unit which includes a PCMCIA port forreceiving the PCMCIA card.
 17. The apparatus of claim 16, wherein theportable computing unit includes a touch-sensitive screen, and theportable computing unit receives descriptive data from a user via thescreen.
 18. The apparatus of claim 17, further comprising a pointedwriting instrument for entering the descriptive data.
 19. The apparatusof claim 17, wherein the portable computing unit comprises a memory andis adapted to alternately record in the memory the descriptive data fromthe user and numerical data from the second signal which numerical datarepresent a coating thickness.
 20. The apparatus of claim 19, whereinthe descriptive data are defined with reference to a pictorialrepresentation on the screen of an article upon which a coating iscoated.
 21. An apparatus for measuring and recording coating thicknessmeasurements, comprising:an electronic memory; means for obtaining aplurality of coating thickness values with a probe electricallyconnected to the electronic memory; means for recording in theelectronic memory the plurality of coating thickness values; and meansfor recording in the electronic memory a plurality of descriptive dataso that each descriptive data is associated with a respective one of thecoating thickness values and provides information concerning therespective one coating thickness value.
 22. The apparatus of claim 21,wherein the coating thickness values are transmitted to the electronicmemory via a PCMCIA card.
 23. The method of claim 1, wherein thedescriptive data includes textual descriptions of the associated coatingthickness values.
 24. The method of claim 1, wherein the descriptivedata includes an image of an object measured to obtain the plurality ofcoating thickness values.
 25. The method of claim 1, wherein thedescriptive data provides a description of a source of the coatingthickness values.
 26. The apparatus of claim 21, wherein the descriptivedata includes textual descriptions of the associated coating thicknessvalues.
 27. The apparatus of claim 21, wherein the descriptive dataincludes an image of an object measured to obtain the plurality ofcoating thickness values.
 28. The apparatus of claim 21, wherein thedescriptive data provides a description of a source of the coatingthickness values.
 29. The method of claim 1, further comprising the stepof inputting the plurality of descriptive data via an input device priorto recording the plurality of descriptive data.
 30. The apparatus ofclaim 21, further comprising means for inputting the plurality ofdescriptive data.